I don't think you will need a lot of "power" to host the Steem network long-term. You will need a lot of disk space, but disks are cheap. The only difficult things for the node to do is a *replay*. Those currently take about 2 minutes (a joke if you conpare to other blockchain techs). Either way, the underlying technology is soooo awesome, that I don't see a scalability issue in near future.

Oh, btw, on this.piston.rocks, there are actually two witness nodes running in parallel, connected to nginx via fail-over/load balancing. That means, I can update the code and replay the one node, while still serving the traffic with the other node and vise versa :)